This invention relates to an improved conveyor wheel or roller for use in storage racks, roller conveyors and the like, and more particularly to an improved conveyor wheel having a hardened outer body shell which defines an outer annular tread for engagement with a load such as a pallet, and the manufacturing method for the conveyor wheel.
Conveyors and storage racks, and in particular those which have a slight slope so as to provide gravity-urged movement of loads such as pallets and the like, typically employ a large number of roller units which support the load and provide for movement thereof along the conveyor. A fragmentary view of a known storage rack or conveyor unit 11 is illustrated in FIG. 1, which unit includes a frame or track 12 on which a series of roller units 13 are supported. The roller unit 13 typically includes a shaft 14 which is supported on the frame and which rollingly supports a conveyor wheel 16 thereon, the latter being disposed so that an upper surface thereof defines a generally tangential plane which provides for supportive engagement with the underside of a load 17, such as a conventional pallet. An example of such arrangement is illustrated by U.S. Pat. No. 6,435,328, although it will be appreciated that numerous other conventional conveyor or storage rack arrangements employing conveyor wheels are well known, and the improved conveyor wheel of this invention is obviously usable therewith.
The conveyor wheel 16 is widely used in many conveyor applications and, as illustrated in FIGS. 2-3, comprises a curled edge conveyor wheel constructed principally of four components for defining the outer load-engaging surface and the outer raceway for the ball bearings. This design evolved many years ago from a design adopted from the roller skate industry with this curled edge conveyor wheel construction, as illustrated by FIGS. 2-3, the four principal components which define the shell include two identical stamped steel outer ball raceway washers 21 and 22 which are typically case hardened after stamping, a soft steel outer body shell 23 which serves as the wheel""s outer tread and raceway retainer, and a soft steel retainer washer that completes the outer body and assists in retaining the bearing raceway.
The stamped outer ball raceway washers 21 and 22 are identical, one serving as the left hand and the other serving as the right hand component of the outer raceway for confining a plurality of ball bearings 26, the latter being engaged with an inner bearing race 27 defined on and surrounding a support hub or sleeve 28, the latter constituting the inner bearing race member. The outer shells or parts 23 and 24 are assembled over the bearing raceway washers 21-22 and are thereafter die struck so as to curl the outer edge of outer body shell 23 over the outer edge of retainer washer 24, whereby the soft outer shell 23 thus holds the entire wheel arrangement together.
Considering the above construction in more detail, the outer body shell 23 and retainer washer 24 have respective arcuate annular inner rims 31 and 32 which cooperate to define the outer bearing race for confining the ball bearings 26, and the arcuate inner rims 31-32 respectively join to annular walls 33-34 which project radially outwardly, which walls 33-34 at their radially outward ends flare outwardly away from one another. The radial wall 33 of the outer body shell 23 in turn joins to an annular outer wall 36 which extends transversely throughout the width of the conveyor wheel and hence defines a tread which is of a generally cylindrical configuration for contact with a load. The outer free edge of the outer wall 36 is then suitably stamped by being deformed radially inwardly so that there is defined the curled edge 37 which wraps around the outer annular edge of the retainer washer 24 to hence maintain the overall housing structure in a fully assembled and confined condition.
Because the outer body shell 23 must be stamped and deformed during assembly so as to create the curled flange 37 which retains the housing in an assembled condition, the outer shell 23 and in particular the outer tread 36 thereof must necessarily be of a soft steel in order to permit the die forming thereof during assembly. Furthermore, once the wheel housing is assembled with the bearing balls 26 contained therein, subsequent hardening can not be feasibly carried out since such hardening would damage the already hardened balls 26 and ball raceway washers 21-22.
The conveyor wheel 16 as described above, even though it has been and continues to be used in many conveyor applications, possesses design characteristics that have been observed to contribute to early failure and high cost. For example, it has been observed that a conveyor wheel in accordance with this design does not have a long life cycle when utilized in use applications involving heavy loading, impact loading and/or intrusion by nails protruding from the bottom boards of wooden pallets that are being conveyed over their surface. The soft steel of the outer housing shell 23 has been observed to collapse, causing the outer ball raceways 21-22 to spread apart, thereby allowing the ball bearings to fall out of the assembly and resulting in complete bearing failure as well as failure of the conveyor system.
In situations in which there is a need to provide a conveyor wheel having a hardened outer body shell, attempts have been made to use a conveyor wheel of the type illustrated by FIG. 4. The known conveyor wheel 41 of FIG. 4 is defined principally by two stamped and hardened wheel shells 42 which are normally of identical construction and disposed and secured back-to-back. The wheel shells 42 define inner arcuate rims 43 which define an outer bearing race for the ball bearings 26, and these inner rims 43 join to surrounding and radially outwardly projecting annular walls 44 which, during assembly, substantially abut and are fixedly secured in a conventional manner, such as by rivets 46. The radial walls 44 at their outer edges are appropriately deformed through substantially 90xc2x0 corners to define transversely projecting outer flanges 47 which, when the two wheel shell members 42 are assembled, project axially in opposite directions so that these flanges 47 hence define the outer load-engaging tread of the conveyor wheel. With this construction, however, the load contact area defined by the outer wheel tread (as defined by the pair of flanges 47) is of reduced contact area due to the annular groove 48 which necessarily occurs due to the manner in which the flanges 47 are formed. This groove 48 hence effects a significant reduction in the load-bearing contact area defined by the wheel. Still further, the flanges 47 normally terminate in free edges 49 which are sharp, particularly at the corners thereof, and it has been observed that these sharp edges 49 can cut into and severely damage the load which is engaged with the conveyor wheels, particularly when the load tends to be displaced transversely relative to the conveyor wheels. Also, these edges can hang-up on the loads and prevent the loads from being sidewardly displaced. Accordingly, while wheels of the type illustrated by FIG. 4 have been utilized in an attempt to provide a hardened annular tread, they nevertheless have not proven totally satisfactory in all applications, particularly those involving side movement or side transfer of the loads.
There thus remains a need in the conveyor industry to provide a conveyor roller/wheel having an outer body shell with an appearance and surface similar to that provided by the traditional roller of FIGS. 2-3, but having a hardened outer body shell which provides a significant annular tread for defining a wide contact area, but which is capable of providing wear and durability, such as when handling impact loads or loads where pallets have protruding nails that impact the conveyor wheels. The present invention thus seeks to satisfy this need and provides a hardened conveyor wheel having a smooth and generally cylindrical annular tread of substantial width and contact area so as to facilitate lateral offloads thereon, while providing substantially increased wear and life, and additionally minimizing damage to the loads. The present invention is believed to provide significant advantages in function, manufacturing costs, and appearance, and the wheel and the process for manufacturing the wheel according to the present invention allows for hardening of the principal wheel parts prior to assembly thereof, while at the same time retaining desired performance and function characteristics.
According to the present invention, there is provided a simplified construction for a conveyor wheel wherein the outer shell of the wheel is formed from two identical shell members which can be identical stampings, with these stampings being hardened and then riveted together to define the assembled shell. The stampings when riveted together are disposed in opposed relationship, and the stampings have inner arcuate raceways which directly define an outer raceway for the bearing balls. The shell members have outer transversely oriented opening channel parts which, when the shell members are fixed together, have the open channel parts aligned and abutted to define a generally closed tubular cross section which defines the rim of the wheel. The channel parts have outer flanges which effectively abut and define the outer annular tread of the wheel, the latter being substantially cylindrical to provide a smooth and flat cylindrical surface having a substantial contact area with a load, with the edges of the tread being rounded so as to prevent damage to the load or hang-up of the load, thereby allowing the load to be displaced or dragged sidewardly over the wheels. With the improved conveyor wheel of the present invention, the overall design is simplified inasmuch as it uses basically only two identical steel parts to define the shell, which two steel parts are defined by the same stamping, thereby simplifying the amount of tooling required, thereby simplifying overall assembly, and hence minimizing the costs associated with making and maintaining tooling and related production equipment.